Fractional distillation apparatus



Patented Aug. 26, 1952 2,608,387 FRACTIONAL ms'rlLLA'rIoN APPARATUS YDavid Geoffrey Randall, Kenley, England Application August 15, 1949,Serial No. 110,438

' InVGreat Britain February 19, 1947 This invention relates to apparatusfor fractional distillation in which use is made of a "wetted-wall"column, Wetted-wall columns have hitherto been utilised mainly forexperimental work and have generally employed a tube or tubes for thefractionating surfaces. Althoughv in such columns the fractionatingeillciency depends upon a number of factors, it may broadly be statedthat the fractionating efficiency is an inverse function of the diameterof the tube. The very small tubes which are required to obtainhigh-fractionating elciencies cannot easily be installed in a plant ofcommercial dimensions.

This arrangement is also uneconomic in view of 1 the small percentage ofthe total cross sectional area, of a column structure employing a largenumber of small tubes, which may be effectively utilised in practice.Another diiculty is the control of the distribution of thereilux on tothe operative surfaces of the column.

The object of this invention is to provide an improved apparatus forfractional distillation and a simple form of fractionating equipment ofthe wetted-walltype, for commercial distillation plant.

In accordance with the invention there is provided apparatus forfractional distillation comprising a casing, a plurality of verticalplates. mounted in said casing in parallel relationship and in closeproximity relative to the cross-sectional dimensions of the casing, andcooling means comprising hollow ducts for carrying cooling uid inheat-conductive relation to the upper ends of the plates to effectselective condensation of any desired pro-portion of vapor risingbetween the plates, whereby condensate formed in the cooled region willliow down both sides of the plates to form a wetted wall column.

The cooling of the vapour is eiected by fluid which is caused to flow ina circuit which passes through or over the upper ends of the plates.

Preferably the fluid is circulated at high velocity through a closedcircuit, part of which is in heat-conductive relation to the luppermostends of the said plates, whereby a substantially constant temperature inthe cooling fluid is maintained in the vicinity of the plate structure.

Referring now to the accompanying drawingr in which embodiments of theinvention are shown by way of example:

Fig. l is a diagrammatic arrangement of apparatus according to oneembodiment of the invention;

Fig. 2 is a perspective view of one form of condensing head of the platestructure;

3 Claims. (Cl. 257-44) Fig. 3 is a part sectional detail elevationshow#l ing the .plate assembly; l i

Fig. 4 is a part sectional view of a modified form of plate assembly;and i Fig. 5 is a part sectional detail elevation further modifiedcooling duct construction.

In the embodiment of the invention shown inA Figures 1, 2 and 3 a seriesof flat plates `l ofV a predetermined area are located in` parallel ar`rangement, and closely spaced relative to the cross-sectionalldimensions of the column. The said plates are mounted in a casing2,5which closes the sides of the plates thus forming a series of whatmay be termed vapour flues. which are rectangular in cross section. Thespacing of theI plates may be achieved in any convenientmanner. Theupper ends of the plates are spaced apart by attaching the plates at setintervals on tubular ducts 3 which .pass transversely through the saidplates. The said ducts are arranged to lie parallel in a horizontalplane and are located. by spacing collars 4. The arrangement is prefer-`ably such that the plate assembly can be dismantled at Will for cleaningpurposes, and for this purpose the plates and collars are retained onthe ducts by the nuts 5. `Where the area of the plate demands it,additional spacing means may be provided by forming ribs, dimples orother projections on the plates which will serve to keep the platesapart and to prevent them` from buckling.

The inlet and outlet ends of the transverse ducts are connected byunions 6 to header` tubes,

1, 8 of a closed circulating system incorporating" a pump 9. In thisexample the said system also` includes a heat exchanger l0 adapted tolower the temperature of the cooling lluid in use to the requiredcooling temperature. external source is passed through the other side ofthe heat exchanger in order to maintain the temperature of the coolingfluid at the required level. Preferably, the pump is adapted tocirculate the cooling medium at a relatively high velocity so that thecooling uid flowing through the transverse ducts has a more or lessconstant temperature. Thus latent heat transmission will be more or lessequal on the surface of all the plates forming the wetted-wall column.

A wetted-wall column constructed as above can be associated with anydesired form of distillation plant, and allows the vapours to risebetween a plate structure whose operating surfaces, being in relativelyclose proximity, provide a very high fractionating eiciency. Moreover,the effective utilization of the total cross sectional area of theCoolant from an aeoasev' 3 column is limited only by the thickness ofthe plates employed, since both faces of the plates form operatingsurfaces. Furthermore, a uniform distribution of reflux is induced onthe operating surfaces by the cooling medium in the horizontal coolingducts which causes condensation of the requisite amount of vapour,substantially before the vapour reaches the ducts. The latent heat isconducted through the vupper endY of each plate, through Athe wallsoftheducts .and hence to the cooling medium. If the said medium iscirculated at a relatively high velocity as aforesaid the effect of `thetemperature. gradient inthe medium as it passes through the ducts issubstantially overcome, and a very high -iilm'co-e'iiicient of heattransfer is obtained.

This very high film co-eflicien't is, in fact, .essential to thesolution of the difiicult heat-transfer problem whi-ch this inventionaims tofsollve: although there is no visible distinction between the;vcondensing- Aand fractionating surfaces, the former may, nevertheless,beregarded 'as the' ex. tendedsurface of. a-heat-.exchanger simi-lar tothe gilled tube type which is L*mest commonly used forI air'heating.v

It will-:be.appreciatedthat the platesneed not be;4 nat: but; may becorrugated: or otherwise shaped: ytheyrfmay: alsof-beiperforated or madeof wire meshv or: expanded Vmetal- Moreover, although substantiallyrectangular platesxarek the. most convenient, theY :invention is not`limited. to thisgshape. TheI whole fractionating equipmentcombinesyhi'gh eiiiciency :with simple :construction and; givesease-,Lof maintenance fandservicing; It, is. also easilyj :dismantled`for :cleaning purposesvr which4 is. of;considerable importance 1inapparatus. of this rtyepe.

The-.arrangement vofi-the ductsmay ibeamo diied` inl latvarliety foffways'and Ythey-.may :run along.' the' upper. edgesofthe: plates. The-du'cts'mayfbe of any desired crossese'ctionalshape. They may. be'formed integrally nr .detachably.fon` lthefupiper; pants .ofthexplates;` Where'theductshaversuffilcientfcondensingxsurface,.theyneed-not b'efintee gralifpartsaof; thez'plates but can abe mounted in'.close.heatsconductive association.` therewithso that ta-nyfpart "of,themeluXfwhi-ch c'ondenses on" the ductssurfaces willowlevenlyiover the:plates:A In. Fig. 'a construction isfshown 'witl-r longitu-ldinalducts' LIj formed. along 1 the" upper edges'f'of the plates bybending the plates over v-int'ov trian'fgnl'arfcrossesec'tional;shapeandweldingfalongthe jointJIZ.- :Suchziducts 'maybe formedl separately andiwelded on to 'the plates rer'mounted limmedately-abovetherm Y y .insa modication, the. `pla't'e'sf:are `attached to, orfassociatedwith'; 'ai cooling? -tanl'nor equivalentmeansf.. which effect :forms a headerf tank;

Cooling medium is induced to flow through said tank and distillationvapour can be led up through the tank and/or laterally as desired.

A single tank common to all the plates may be used or it may be dividedup into compartments or ducts. In Fig. 5 a header plate I2 is machinedon both faces to form ducts I3 on the upper side, which are closed by acover plate Ill, and inclined condensingfaoes |15 on the underside. yThelatter isgrooved-ito*receive the-upper edgesof the plates and vapourpassages I6 are formed through the plates I2 and I4. The plates may ormay not be secured to the .header plate. It will be understood'the platecould be fabricated or formed of -icorrugated @plate'zinstead of beingmachined from prising `awcasing', a plurality of. vertical':platesAmounted :in saidcasing .in parallelclosely spaced rela-tionship,. andcool-ing.:meanscomprisingholglowcoolant l'ductsfin-fheat-conductive.contact with:

theupper ends only-fof lsaid plates A.tofeffectfselech- Y tivecondensatienof Lany :desired fpiorftion ofj Iva-por.

rising between fsaid.;plates whereby condensate formed in then cooledregion will iiow dow-n Jeoth-Y sides :of .thefplates tof formylelf-wetted `wall columrr. 2. .Apparatus v'as defi-ned -in claim 1wherein fthe;

cooling :means comprises. a. plurality-of coolant; ducts: positioned .inia. .horizontal Aplane fand 'exetending: parallel -to andinl heatconductive cori-n tactfwitlfr'the'upper endszonly-fof said'plates- V Y3. Apparatus fas denedrin claim 1-where`inzthe: cooling.-meansdcomprises `a 4v:plurality '1 of. coolant ducts positioned inai..horizontal pla-ne* and-.exT

tendingl ltransverse toland :in ,fh'eat/ nconductive contact- `with theupper ends :only` of. said plateszv.

DAvmwGneFnaEYRANnALL. l

REFERENCES CITED i'lleV Lof this fpa'ltent :f-

'UNITED' STATES .PATENTS

1. APPARATUS FOR FRACTIONAL DISTILLATION COMPRISING A CASTING, APLURALITY OF VERTICAL PLATES MOUNTED IN SAID CASING IN PARALLEL CLOSELYSPACED RELATIONSHIP, AND COOLING MEANS COMPRISING HOLLOW COOLANT DUCTSIN HEAT-CONDUCTIVE CONTACT WITH THE UPPER ENDS ONLY OF SAID PLATES TOEFFECTS SELECTIVE CONDENSATION OF ANY DESIRED PORTION OF VAPOR RISINGBETWEEN SAID PLATES WHEREBY CONDENSATE FORMED IN THE COOLER REGION WILLFLOW DOWN BOTH SIDES OF THE PLATES TO FORM A WETTED WALL COLUMN.